FIGURE 1.

Effects of Lsb proteins on [PSI⁺]. A, [PSI⁺] destabilization by HS. B, lsb1Δ affects [PSI⁺] destabilization during HS. In panels A and B, yeast cultures were grown to early exponential stage at 25 °C, shifted to 39 °C for the specified periods of time, plated on YPD and incubated at 25 °C. [PSI⁺] (pink), [psi⁻] (red), and mosaic [PSI⁺]/[psi⁻] colonies were detected by visual inspection. The percentages of colonies in which prion was destabilized by heat shock (red [psi⁻] and [PSI⁺]/[psi⁻] mosaic) are indicated. Averages of six experiments are shown with error bars correspond to standard deviations. C, the lsb1Δ and/or lsb2Δ do not affect viability of the exponential [PSI⁺] culture at 39 °C. The control strain LSB1, LSB2 (OT55), and isogenic lsb1Δ and/or lsb2Δ strains were pre-grown at 25 °C, and aliquots were placed at 25 and 39 °C. Serial decimal dilutions were prepared after the indicated periods of time, and 2.5 μl of each dilution were spotted onto YPD medium. Plates were photographed after 6 days at 30 °C. D, analysis of the first cell divisions after HS at 39 °C. After resumption of cell division, mother and daughter cells were separated by micromanipulation. Only pairs where both mother and daughter were viable are presented (for viability data, see Table 2). For each type of mother/daughter [PSI⁺] distribution, numbers are shown. The probability of random deviation of the observed results from those expected in case of equal segregation of [PSI⁺] between the mother and daughter cells, calculated by using the χ-square approach, is indicated.